The problem of corrosion of metal surfaces in contact with various corrosive materials is well known. Most acidic liquids or compositions comprising same will cause corrosion when in contact with metals. The extent of such corrosion will, of course, depend to a large extent on the system on or in which the acidic material is to be used or upon the environmental conditions of such use.
In the area of coating metals, a clean surface is a prerequisite to a quality coating. Grease, metal oxides, including scale, shop dirt, will adversely affect the adhesion, continuity and permanence of the coating by acting as a physical barrier which prevents proper bonding of the coating to the metal.
Metal surfaces can be cleaned by solvent, solvent emulsion, alkaline cleaners, solvent vapor degreasing, or abrasive blasting. Conventional cleaners will not remove scale and oxides from metals. Thus, it is necessary sometimes to use an acid cleaning treatment (pickling) to remove rust and other corrosion products. However, the acids generally used are corrosive and must be rinsed from the surface once it has been cleaned (see U.S. Pat. No. 3,973,998).
The need exists, therefore, to inhibit the corrosive effects caused by these acid cleaners. Conventional corrosion inhibitors which can be incorporated into an acid cleaner include compounds such as thiourea, propargyl alcohol, toluidene, triphenylsulphonium chloride, pyridine and hydroxyalkylthiosubstituted polycarboxylic acids (U.S. Pat. No. 4,670,163). The drawbacks many of these corrosion inhibitors exhibit are that they may be either toxic, flammable, carcinogenic, non-biodegradable or harmful to aquatic life.
Accordingly, an object of this invention is to provide a composition which can be applied to metal surfaces to inhibit corrosion and pitting of the metal without the attendant deleterious side effects of conventional corrosion inhibitors.